1. Technical Field of the Invention
This invention relates to intraocular lenses (IOLs), which are to be implanted in the eye to replace a natural lens that has been removed because of cataract or other reasons. More particularly, this invention relates to an IOL with an uniquely-shaped haptic designed to be implanted in the anterior or posterior chamber of the eye.
2. Background of the Invention
There are many IOLs of varied shapes on the market, which are used to replace the natural lens of the eye after surgery where the natural lens of the eye is removed. Such lenses include an optical portion and one or more support loops or sheet-like haptics, which retain the IOL optic in the eye in its desired position either in front of the iris in the anterior chamber or to the rear of the iris in the posterior chamber.
The haptics retain the IOL in a relatively fixed position so that light can be focused on the retina. It is advantageous for the haptics to be flexible in order to accommodate changes in shape of the eyeball without causing damage to any of the interior portions of the eye in contact with the haptics.
IOLs can be formed of a single-piece of material such as polymethylmethacrylate (PMMA) where the haptics are formed integral with the optic portion through casting, machining or lathe cutting methods. Other types of IOLs, called multi-piece lenses, can also be formed where haptics made of a material such as polypropylene or PMMA are attached to an optic portion by heat welding or through laser welding, ultrasonic welding or other methods.
More recently, IOLs have been formed of so-called "soft" materials such as hydrogels, acrylics or elastomers. Examples of such materials are described in U.S. Pat. No. 4,573,998. The present invention is particularly adapted for use with IOLs formed of such soft materials.
IOLs are formed with flexible support members or haptics in order to facilitate positioning of the lens in the proper location while accommodating changing shapes of the eyeball. The haptic design, including its flexibility, is considered to be important in achieving maximum patient comfort and lack of postoperative complications, ease of implantation and effectiveness of maintaining the lens in its proper position.
The haptics or IOLs formed of the so-called "soft" materials have haptics that are sheet-like or substantially flat, which are formed integral with the lens optic. It is important that the haptics are sized so that they fit accurately and snugly into the eye of the patient. Typically, a surgeon must have available a large inventory of lenses wit haptics of different sizes so that he can accurately fit the lens to the particular eye on which he is working. This is an expensive requirement. It would be beneficial to have a single lens which could fit any size opening in order to obviate the requirement for a large inventory of surgically clean lenses.
Attempts have been made to provide one lens which has adjustable haptics so that a single lens can be used to fit a wide range of eye openings. One such attempt is illustrated in U.S. Pat. No. 4,134,161. This lens has a stationary haptic having two toes on one side of the lens while the other side of the lens has an adjustable haptic having two toes. The adjustable haptic can be moved in or out with respect to the optic portion of the lens, thereby adjusting the overall outside dimension, measured from toe to toe, of the lens. Adjustment is achieved by providing ridges and grooves on the adjustable haptic which mate with ridges and grooves on a stationery portion of the lens. Once the desired adjustment is made, the adjustable haptic is held n position by means of clamps which force the mating ridges and grooves together. This arrangement requires that manufacture of the lens include formation of relatively intricate moving parts having small interlocking features. Some of the parts having smaller cross-sections, such as the clamps, are subject to breakage either during installation or after a period of use.
Another attempt at making an adjustable lens can be seen in U.S. Pat. No. 4,296,501. This lens has an L-shaped stationary haptic on one side of the optic portion while the other haptic on the other side of the optic portion is formed of two connected arms, the second of which can pivot about its connection with the first arm. By means of pivoting the second arm, the surgeon can adjust the overall outside dimension of the haptics, from toe to toe, to the desired dimension for the eye being worked on. Once the second arm is in the desired position, it can be sutured in place by means of holes provided in both arms. This lens, again, requires somewhat complex manufacturing procedures to provide a lens having relatively intricate interlocking parts which can move with respect to one another. The mating of the rotating arms of the second haptic is achieved by reducing the thickness of these arms. The sections of reduced thickness are held in the desired orientation by attachment means such as suturing at a small number of attachment points, such as the holes provided. In order for this adjustable haptic to be sufficiently rigid to hold the lens in place, the attaching together of the pivoting arms must be tight and permanent. The pivot point, therefore, being of reduced thickness and utilizing only a few attachment points, is the weakest portion of the haptic structure. Any fatigue of the sutures or plastic parts will result in breakage or at least loosening of the attachment between the pivoting arm and the stationary arm. This will result in a loose haptic which will allow the lens to become dislodged.